This invention is generally directed to imaging members, and more specifically, the present invention is directed to members comprised of a single bipolar photoconductive layer containing, for example, a mixture of charge generating components, or particles, and charge transporting components, such as charge transport molecules, electron transport components, and a binder, and wherein the charge generating components are sensitive, for example, to a wavelength of from about 400 to about 950 nanometers.
More specifically, the single bipolar layered photoconductive imaging members of the present invention can be selected for a number of different known imaging and printing processes including, for example, multicopy/fax devices, electrophotographic imaging processes, especially xerographic imaging and printing processes wherein negatively charged or positively charged images are rendered visible with toner compositions of an appropriate charge polarity. The imaging members as indicated herein are in embodiments sensitive in the wavelength region of, for example, from about 650 to about 950 nanometers, and in particular, from about 700 to about 850 nanometers, thus IR diode lasers can be selected as the light source. Moreover, the imaging members of the present invention can be selected for color xerographic imaging applications where several color printings can be achieved in a single pass.
The imaging member layer components, which can be dispersed in various suitable resin binders, can be of various thicknesses, however, in embodiments a thick layer, such as from about 5 to about 60 microns, and more specifically, from about 10 to about 40 microns, is selected. This layer can be considered a dual function layer since it can generate charges and transport charges over a wide distance, such as a distance of at least about 60 microns. Also, the presence of both the electron and hole transport components in the photoconductive layer can enhance mobility of both electrons and holes, and thus enable the imaging member to function with positive or negative charging conditions. As a result, the single bipolar photoconductive layer is capable of transporting both positive and negative charges rendering it more versatile than the photoconductive device with unipolar, either hole or electron, transport properties.
A number of electrophotographic imaging members are considered multi-layered imaging members comprising a substrate and a plurality of other layers such as a photogenerating layer and a charge transport layer. Typically, the charge transport layer contains one kind of charge transport components, either hole or electron transport molecules, and hence the member is unipolar and will operate under one type of charging process. Furthermore, the photogenerating layer tends to be very thin, about 1 micron or less, to allow photogenerated charges to be injected out promptly into the charge transport layer. The thin photogenerating layer is substantially incapable of fully absorbing imaging laser light leading to the formation of an interference pattern, namely “plywood”, in the printed outputs. These multi-layered imaging members are, therefore, costly and time consuming to fabricate because of the many layers that must be formed. Further, complex equipment and valuable factory floor space are required to manufacture these multi-layered imaging members, and moreover, some of these members possess undesirable plywooding affects. The expression “plywood”, refers in embodiments to the formation of unwanted patterns in electrostatic latent images caused by multiple reflections during laser exposure of a charged imaging member. When developed, these patterns resemble plywood.
Hence an additional anti-plywooding layer may be needed below the photogenerating layer to scatter the laser light to prevent the formation of plywood pattern. Various approaches are known to eliminate the plywood effect, such as roughening the substrate surface, introducing light scattering particles, and adding a light absorbing layer below the photogenerating layer.
The single bipolar photoconductive layer, which can be exposed to light of the appropriate wavelengths simultaneously, or sequentially, exhibits excellent cyclic stability, independent layer discharge, acceptable dark decay characteristics, excellent residual voltage, allows tuning of the electrical properties of the imaging member, excellent photosensitivity, and enables substantially no adverse changes in performance over extended time periods. Processes of imaging, especially xerographic imaging and printing, including digital, are also encompassed by the present invention.
Imaging members with single bipolar photoconductive layer possess a number of advantages as indicated herein, however, the complex interactions between photogenerating components, charge transport components and polymer matrix binder may impose constraints in the design of these members, especially with regard to optimizing the photosensitivity of the number for a particular application. In contrast, with the present invention in embodiments there is selected a mixture of two photogenerator pigments in single bipolar photoconductive layer, as a means for adjusting the photosensitivity of the imaging members over a wide range and achieving excellent predictability of the photosensitivity two pigments with different photosensitivities, for example one that is about 2.5 times more sensitive than the other, can be selected in embodiments of the present invention, for example a mixture of Type V hydroxygallium phthalocyanine and x-metal free phthalocyanine.
Thus, there remains a need for improving the color printing capability of xerographic processes, and in particular, to permit the printing of a number of colors with a minimum number of photoconductive passes, and therefore, for example, enhance the productivity of the printing process; and moreover, there is a need for single layer photoconductive imaging members with excellent photoconductor electricals and a wide range of photosensitivities.
These and other needs and advantages can be achievable with the photoconductive imaging members of the present invention in embodiments thereof.